Acoustic device



April 13, 1948. Y H.' HoRNE r 2,439,736

' AcUsTI DEVICE Filed Feb'. 1o, 1944" 9 sheets-snaai 1 3C '5b /7 Z b ajj/mljNl/ENTOR.

BY 7770er,

AonNeYs April 13, 194s. H. Home A 2,439,736

, ACOUSTIC DEVICE Filed Feb. 1o, 1944 9 sheets-sheet 2 M #my INVENTOR.

HTTORNEYS April 13, 194s. H. Home i 2439,73@

AcosTI-c DEVICE Filed Feb. 1o, 1944 9 sheets-sheet 3 1 VENToR.

BY wm a,

.HTTORNEYS H. HORNE ACOUSTIC DEVICE April .13, 194s.

Fil'ed Fei. 1o, 1944 9 sheets-sheet 4 INVENToR, 074%/ ATTORNEYS H. HoRNE ACOUSTIC DEVICE Filed Feb.' 1o,` 1944 April 13, 1948.

9 Sheets-Sheet. 5

IN VEN TOR. l #M/m Y ATTORNEYS April 13, 194s. H. HORN; I 2,439,736

ACOUSTIC DEVICE Filed Feb. l0, 1944 9 SheetsSheet 6 ATTORNEYS April 1s, 1948. H. HORNE 2,439,736

AcoUsTIc DEVICE Filed Feb. 1o, 1944 b sheets-sheet 7 /TTORNEYS April 13, 1948. v H, HQRNE 2,439,736

Acousrlc DEVICE Filed Feb. 1o, 1944 9 sheets-sheet a H TTORNE YS April 13, 1948. H. HORNE l 2,439,736

ACOUSTIC DEVICE Filed Feb. 10,. 1,944 9 sheets-sheet 9 INVENTOR.

BY M

ATTORNEYS Patented Apr. 13, 1948 Hal Horne, New York, N. Y.

Application February 10, 1944, Serial No. 521,816 A This invention relates sound generator and sound modifier which can be used as a musical instrument, and for various other purposes.

Oneof the objects of this invention is to prof vide a precision instrument for this purpose.

Another object of this invention is tocompensate for the fact that` it is impossible commercially to manufacture the outer shells which constitute the casing of this instrument,` with.`

suiiicient precision to produce shells which are substantially alike.

Another object of this invention is to divide the air space between the shells into aplurality of air columns.

Another object `of this invention is to .produce a device which has a casing which consists of a plurality of outer shells, and which also has an internal diaphragm. Said internal diaphragm may be made of resilient metal or a suitable resilient alloy.

Another object of this invention is to provide to a new and improved Claims. (Cl. llr6-178) Fig. 8is a sectional viewalong the line 8-8 of Fig. 7. L i

Fig. 9 is a view similar to Fig. `1, of

embodiment of the invention. i

Fig. 10 is asectional view on the line Illl0u of a fourth Fig. 9.

Fig. 11 is a view similarto Fig. 1, of a nfthembodiment of the invention.

Fig. 12 is a sectional view on the line I2,|2 of Fig; 11.

Fig. 13 is a vertical sectional view of a sixth embodiment of the invention.

Fig.` 1451s a partial sectional view, which illusi 'trates `a seventhembodiment of the invention.

Fig. 15 is a sectional view on the line l5`|5 of Fig. 16.

a device in which said diaphragm will have a plunger vibration or movement and plunger ac- ,.tion, in order to secure best results.

Another object of this invention is to provide means whereby the internal diaphragm is anchored to one of the outer shells, in such manner as to avoid or minimize any leakage at the point of anchorage. Another object is Ato provide a musical instrument which can produce various unique tonal eiiects bylan unskilled person.

Numerous additional important objects of the invention will be stated in the annexed descrip- Fig. 4 is a partial top plan view'of` the bottom shell of Fig. 3, taken along line 4--4 of Fig. 3.

Figs. 5 and 6 are views similar to that. of Fig. 4, showing variations of the shape of the bottom shell.

Fig. 7 is a View similar to Fig. 1, of a third embodiment of the invention.

Fig. 7A is a sectional View along Vthe line 'lA-1A or Fig. 7.

Fig. 16.is a partial topplan View, similar to Fig. 1, of an eighth embodiment `of the invention.

Fig. 17 is a partial top plan view of a ninth embodiment of the invention. M

' Fig. 18 is a section-al View on the line l8-l8 of Figjl?.` i

Fig. 19 is a top plan view similar to Fig. 1, of a tenth embodiment` of the invention.

Fig. 20`is a sectional View `on the line 20--20 oi Fig. 19.

Fig; 21 is" a. sectional View, similar toFig. 20, of an eleventh'embodiment of the invention.

Fig. 22 isa top plan viewsimilar to Fig. l, of a twelfth embodiment of the invention.

Fig123is a sectional viewfon the line 23--23 0f Fig. 22. A

Fig. 24 isa section on the line Q -24 of Fig. 23. Fig. 25 is a partial View which illustrates a modication of the internal diaphragm, showing that'said internal diaphragm can'be provided with la scalloped edge.

Figs. 26 and 27 are respective sectional views which illustrate additional embodiments Voi the invention.

Fig. 28 `is a sectional view of another embodiment.

Fig. 29 is apartial top planview ofthe diaphragm shown in Fig. 28.

The device shown in the embodiment of Figs. `1

and 2 comprises outer shells Vor'casing members I and2. These casing members I and 2 can be made of resilient non-metallic material, as disclosed in U. S. Patent No. 2,274,897, issued on March 3,194.2.` Said outer shells I and 2 can be made of' any metallic or non-metallic material, which Acan be either resilient or non-resilient. Only one of said shells, such as the shell' I, can be resilientor resonant, so that the shell 2 can be ,sufficiently` rigid `to be non-resonant or substan- 3 Y tially non-resonant. Both shells I and 2 can be rigid and non-resonant.

The line 2 2 of Fig. l indicates the location of the vertical median longitudinal plane of the device. Each shell I and 2 is provided with respective lateral flanges 6a, 6 and 6b, at each side of said median vertical longitudinal plane. The respective anges 6a, Ii and 6b are identical in both shells, so that the partial illustration of said flanges in Fig. 1 is sufficient. f'

The device has a front inlet portion or lip portion I2, to which the lips of the user are applied.A It also has a rear outlet or throat 3, through' which air escapes rearwardly, when air isgforc'ed f'.' into the device, in the direction of the longitudinal 1,5 arrow which is shown in Fig. 2. Saidrthroat Sis t transversely and laterally tapered, ,so'thatgitsrear outlet end is larger than its front inletend. The inner wall of throat 3 is frusto-conical".

Intermediate the points 4 and 5, the body of 20 theshell-l is'I laterally. andl also. longitudinally arched. The inner wall Ia of the shell I is sub.-

`stantiallyparallel to' the zrespectivee adjacent portion of the outerfwall di'saidshell I.. Each ofi-said inner andfrouterfwalls ofthe shell. I,'.be 25 tween said points 4 and 5, may have they shape ofla partofy a sphere, or any other rounded or arched or concavo-convex shape; l

Each said -innerglwall andouter wall of shell I,

of parts of several Vspheresiof.respective: different radii, in order to .secureor to approximate exf ponential spacing between the inner. wa1l=|a of shell I and `the respectiveinner wall offshell 2, orsbetween the inner wall Iaof. shell Iv and the adjacent wall of the diaphragm l.

The :internal wall of the shell 2 is provided with a recess or depressionzwhich has paralleLlongitudinalV walls 2a at theLliD 'portion- I2.' Rearwardly of said parallelwallszZa; `said` depression f4() has walls I'I which are inclinedV longitudinally towards each other. Said recess of theshel12 has a rounded rear-end I la.`

The internal diaphragm `'I` is madeof veryresilient springy material, such asgPhosphor bronze or any other suitable metal or alloy or nonFmetallic material. The. body of said diaphragm 1, rearwardly of its transverse rib 8, is-both iong` tudinally and laterally arched, so that eachwall of said bodyhastheshape of a partzo asphereg.- or of la cone. Said-body` 1 is preferablyfofz-equal thickness and resilience throughout. If the body of the diaphragm 'I is made of Phosphorjbronze, thetlflickness of said body may be:-.003'.007inch, preferably .005 inch.

Each flangel haslrespective edges I4= and'I4a which are concentric. EachA said edgel4` andMa hasthe shape of a part of a circle; whose center is locatedat thel point I 5;

At the lip portion I2, said angesY 6'; are err-60 tendedV so as to form lateralribs d-fwhich'terminate at the longitudinal edges of the lateral rib 8 of the-diaphragm 1. Thefrespectivefends of said ribs 6d are spaced wlaterally fromthefrespective longitudinal walls #2a.-

As previously stated,` the internal diaphragm 'I` has a body which is both longitudinally-and laterallyarched, so that each -face ofsaid body has the-shape of'a part ofa spheregona part 4of a cone. This invention-isnot limited to this.' 70 as saidzfaces -may have any suitable curvatures and said faces may. have the' :shapes f-ofypartsof cones. Said diaphragm'lhasa peripheral-.dangle I I, which ihas respective;outerrsand inner concenf tric edges f lia' :and 'I I-bi. The-innen edge. IIhof 75 the ange II is a continuous circle, whose center is located at the point I6. The outer edge IIa has the shape of a part of a circle. The respective spaced ends of said partial circle of the outer edge IIa, terminate substantially at the rear edge 8a of the lateral rib 3. Said rib 8 also has a front lateral edge 8b. Said rib 8 is integral with the body l, and said rib S is also integral with a.forwardly extending. planar extension 8c. A rigid stiiening member or rigidbar I0 is suitably fixed to the extension'or projection 3c. The rib 8 has the shape of a part of a cylinder. As shown in Fig. l, the width or lateral dimension offthealateral rib 8 is greater than the width of the longitudinal recess of the shell 2, between its longitudinal parallel Vwal-ls 2a. The lateral ende-portionsfoff extension 8c abut the respective partsof the internal wall of the shell 2. Said internal Wall of the shell 2 is of planar shape, laterally beyond each longitudinal wall 2a. Screws-9 finthestifening member mi to theeinternalwall ofiV the'. shellA 2,I at pointsr Which-- are ois'etllaterallyJ with respect to saldi walls 2a.`v The Shanks of the screws 9 enter suitable tapped -recesses--which arejprovided` in the respective parts/ofi the respective planar parts of-l the: in'- ternalfwalloftheshell 2. The screws 9 therefore do not; interfere withthe free passage fof airthrough the recess which is-provided between between said points 4 and 5, can have theshape 30 the walls.: 2a .inwthe internal wall of' the shelll2, in` the direction of.` theV arrowwhich is shownin Fig. 2. The front and rear edges 8U andc'lof therib-S-f abut the internal wall of.` the-shell 2, laterally atleach sideof the longitudinal :walls 2a.

For convenience, the device will be described with .referencelto- Vits yposition shown in: Figf.'2, in whichthemtop 'and' bottom planar facesnof `the flange 1II-are horizontaL The bottom planar face-,ofthe il'ange. I I abuts the'internal respective annularf horizontal planarA face of. the shell2,

save at the recess between the walls 20;,1so asfto provide'` a seal? which: is Hwholly or` substantially air-tight, save 1 at 1 the i recess ofshell" Tbetweexr the Walls 2a.!

The liner I Ic' in; Fig.2 indicates theV horizontal plane of theifrespective internal: horizontaliace ofshellllandit is clear that the lateraledges Bbf-andra are. inf. thel same plane as'the. plane of the-,bottom or. sealing'fa'ce of thev flange II.v The -botto'm facesofcthe'extension actor the'diaphragm IS islfalsoi in therhorizontali.planezwhich is indicatedby thezlin'e I Ici.' Y

The diaphragm 'I and its ange II therefore normallyfseparate the'v interior 'ofY the casing'into 'two whollyseparate air chambers between'which access isprovided, only wheniutheI diaphragm'l oscillates: Hence,` the :interiori ofi the device Inormally- :hasy `two whollytseparated "air columns. ThereisV a top'air fcolurrln` loetweenu-fwallV Iarand diaphragm l, whichisopen only atfits rearthrough throaty 3. There-is abottom air column between diaphragm I and the respective part of the internalwallY of shell 2.V Sadbottom air-column is normally. open, onlyv at itsv front, through, the recess of'sl'iell`2.'

At its rear end, the shells, Land 2are shaped so as tov provide saidoutlet ror throat3, which has aninternalwall V(ic of Truste-conical shape. Said wallc" tapers outwardly and rearwardly, so that the'rearend'O said wall 5c is ofgreaterA diameter than its front end, Said throat 3 may be of any desired/length. The shells'rI and'Z may be-xed to each other, onlyA atithe-iianges Ea' andftheribs 6d', sothatsuch/shellsV Il and 2 are Vunconnected to each other along their respective" flanges 6 `Tand itsriiange II.

`anidlb of the shells I- and 21ers biased normally `to contact with each other, by the resilience of the shells `I `and'2. ,If shell 2 Vis rigid, the resilience of shell I biases its two flanges 6 and its two flanges 6b, normally to contact with the rer spective flanges 6 and 6b of shell 2. The respective ribs 6d of the shells I and 2 also normally contact with each other. However, when the air columns within the shells vibrate, said shells are free to vibrate in unison with said air columns..`

of the ribs 6d during such vibration. If desired,Y

theribs `6d, of the respective shells can be unconnected to each other, so that the shells are connected to each other only along all oralong anydesired portions of their respective anges 6a. 1 The respective shells I and 2 can also be fixed to eachother along their respective flanges 6 and 6b. Hence I can control the `extent oftemporary separation of the shell I` and 2, atyany parts of their normally abutting flanges. If the shell 2 is made rigid and non-resonant, the permanent connection between shells I'and 2 can be made in any of the previously described ways.

1 The arched shape of the body of the diaphragm 1, dueto its partial spherical shape or its partial conical shape or other arched shape,-

gives said body considerable stiffness, so that said `body `retains said normal arched shape when the diaphragm 1 Vibrates. The convex face of the Arib 8 is located in a corresponding lateral concave recess of` the internal wall of the shell I, preferably with slight clearance between said rib 8 and said recess. Said rib 8 may fit tightly insaid recess of shell I. l

When the user sings or talks into the device,

at the lip portion I2, or when sound waves areotherwise produced, the diaphragm 1 resonates or oscillates while its arched body permanently retains its said normal arched shape. The ange `II moves in unison with said permanently arched body. :Said body 'of diaphragm 1 may vibrate orresonate as a unit, by turning relative to the lateral hinge-line which is provided by the -rib 8. Said lateral hinge-line or hinge- `connection is substantially at vthe rear lateral edge 8a of the lateral rib 8. The rib 8 andV extension 8c remain in fixed position, during the vibration or oscillation of the body of diaphragm Said diaphragm 1 `can vibrate or resonate as a` unit or in sections.

The screws 9 can be applied with suitable pressureagainst the rigid bar Il) and the projection 8C, in order to securely anchor the diaphragm to the bottom shell 2, forwardly of the rib 8. This prevents any lateral shifting of the diaphragm 1, while permitting the arched body of said diaphragm 1 to vibrate up and down, in unisonwith its flange II, so that the diaphragm 1 can operate substantially like a rigid plunger, thus producing the highest efliciency. When the body of the diaphragm 1 is thus vibrated as a single unit, the ange I I is moved in unison with saidbody, relative to the internal wall of the shell 2, so that air can move between the bottom air chamber and the top air chamber, due to the temporary entire or partial raising of the flange II from its normal sealing position.

In addition, the air column in the top air chamber is periodically compressed and rarefied, due to the relative movement between diaphragm I and the shell l.

. iHencethejsound waves which are produced in the bottom air column are'transmitted tothe top air column, by a combined action.. 4Such transmission is produced by the vibration of diaphragm 1, which causes ange Il to move away from its sealing position and back to its sealing position, gwith the consequent compressions an rarefactions of the air. As shown in Fig. 2, the recess which is provided in the internal wall of the shell 2, is of substantially constant and maximum depth between the walls 2a. The depth of said recess is then gradually decreased to zero at the `front rounded end I 1a of said recess. Hence, the depth of the recess is diminished as its width is diminished. along the converging walls I1. The air which is forced into said recess at its front end, is thus forced upwardly at an angle against the body of ithe diaphragm r1f, as `shown by the longitudinal arrow in Fig. 2.

The drawings arersubstantially to scale, so that reference can be made thereto for additional details, such-as the sizes and relative proportions diaphragm 1 must-be loaded by an air column.

'I'his air` column is located in the air chamber rist which is located above the diaphragm 1`. Said upper air column is closed, save at its rear end at throat 3. The curvedlcontour of the internal wall Ia shapes `this loading air column for proper distribution of the sound waves. This design, together `with the plungerflike action of the diaphragm, produces very high efliciency. One of the functions of the air column which is provided above the diaphragm 1, is to' provide ,a coupling between the movement ofthe diaphragm 1 and the movement of the air at the throat 3. The diaphragm 1 itself, even `when it vibrates atits greatest amplitude, doesnot `deliver any great amount of sound energy. Therefore, `the loading of the diaphragm with an upper air column is an important feature. The upper -air column is of small size at its front end; in order to produce an appreciable pressure loadon the diaphragm 1 at its front end, adjacent the lateral edge 8a., between said diaphragm andthe wall Ia, when the upper column is compressed at its front end by a sound wave. This upper loading` air column is enlarged at its rear end, adjacent the throat 3, in order to radiate the sound efficiently, either into the atmosphere, or into the interior of Va tapered magnifying horn which can be connected to the throat 3.

In order to secure maximum eiiciency, the gradual increase in volume of this upper loading air column, from `front to rear. follows an exponential formula. The increase in volume of the upper air column is gradual and continuous,

Vin order to eliminate any reflection of sound waves in said upper loading air column.

If desired, the flange II can beprovided with a series of grooves which are concentric with the point I8, thus providing said flange! I with concentric ribs which normally have a sealing fit against the respective `part of the respective internal planar wall of the shell 2. Said internal planar wall of shell 2- can also be provided with such ribs, which may abut such ribs of dange II.

The points I5 and I6 are located in the vertical median longitudinal plane of the device, which is defined by the line 2-2. The vibrations may be transmitted from the lower air column to the upper, air column, wholly or almost Wholly 9 at its rib, and no part of iiange II is fixed between said shells I and 2.

Infthe ninth embodiment of Figs. 17 and 18, the lip-portion I2 of the bottom shell 2 is provided with an upwardly inclined inlet bore which opens into a recess of shell 2. A pin 31 is iixed A to the arched body of the diaphragm 1. Said pin 31 projects, with very slight clearance, through the top wall of the shell I. At its upper end, said pin 31 is xed to a diaphragm 38, which has horizontal annular corrugations 39. The rim of said diaphragm 38 is fixed to the rim of the shell I` by means of a rigid clamping ring 4I), which isI fixed to the rim of shell I. As previously statedr both shells I and 2 can be rigid and non-reso-` nant. This applies particularly to embodiments like Figs. 13, 15, 13, etc. Y

As shown in Fig. 18, the top cavity of the shell I is provided with a fixed liner L, which is made` of felt or some other sound-absorbing material.

Since the cone 38 is larger than the diaphragm 1, said cone 38 radiates the lower frequencies at high eiiiciency. As inthe previous embodiments, the air chamber between the diaphragm 1 and the adjacent internal wall of the shell I, is `of exponential design. Fig. 18 also shows the throat 3, which is common to shells I and 2, and through which the high frequencies are radiated. This type of instrument has an extremely large frequency range. The high frequencies can be amplied by means of a suitable amplifying exponential horn which can be connected to the exponential throat 3.

The tenth embodiment of Figs. 19 and 20 `is substantially the same in principleas Athe rst embodiment of Figs. land 2. In this tent-h embodiment, the internalwalls of the shells I and 2 are shaped to provide a common inletfbore 14311;.

For this purpose, said Ainternal walls have equal recesses. VSaid internal walls of shells I` and 2 arealso shaped to `provide a commoniongitudinal partition 43. The Vrespective anges II of the respective diaphragms 1 divide the interor of the device into three air chambers. 'I'he central air chamber is located between the two diaphragms 1. chambers have respective outlet throats 3. The tenth embodiment deliverssound of greater volume than the rst embodiment. AIn the tenthV embodiment, the respective diaphragms 1 are identical.`

Whenever I provide a single diaphragm, or a plurality of'identical diaphragms, `each said diaphragm may have a natural frequency which is in the normal audible limit, or such natural frequency may be above or belowthe audiblelimit.

In the eleventh embodiment of Fig. 21, the respective diaphragme 1 areidentical. This eleventh embodiment has an internal partition 42 and the inlet 4I has an internal truste-conical wall whose Width decreases rearwardly. `A single throat 3 is provided.

In the twelfth embodiment of Figs. 22,` 23, and 24, I provide two diaphragms, each of `which has a respective frequency which is within the audible limit.

The natural frequency of the bottom diaphragm,

of Fig. 23 is higher than the natural frequency of they top diaphragm. `Hence the higher'frequencies are emitted, largely orA wholly by the bottom diaphragm, and the lower frequencies are emitted largely or wholly by the upper diaphragm. An acoustic dividing network can `be used here to make the division between the two frequency ranges more positive. The partition 42a offFig'.

'Ihe top and bottom` air,

` into a. plurality of air chambers.

Y pressing the knob 45a, thus moving itsshank 23 generally corresponds to the partition 42 of Fig. 21. The partition43 of Fig. 20, the partitionv 42 of Fig. 21 and the partition of 42a of Fig. 23 can be made of flexible or resilient material also, of a thickness which permits each said partition to vibrate.

Fig. 25 shows that the continuous flange I I can be replaced by separated flange sections IIa; Thisl scalloping of the ange produces a softer sound. A

Fig. 26 shows that the diaphragm 'I can be biased by means of a blade spring 44, whose upper end is lixed to the shell I so as to increasethe force ywith which the diaphragm 1 normally or permanently divides the interior of the device Such biasing spring also imposes an additional load on the diaphragm.

Fig. 27 shows that the upper leg of said blade spring 44 is fixed only at its free end tothe shell I." Therefore, the biasing pressure of said spring 44 against the diaphragm can be regulated by dethrough a bore of xed plug 45h, thus increasing the load on the diaphragm. If the knobl45a is released, the pressure of its shank on the spring 44 is decreased to zero. The biasing compression spring 45 normally holds knob 45a in such position that its shank exerts no pressure on spring 44. This adjustment of pressure on spring 44 can be made at will While playing the instrument.

In every embodiment described herein, the outer shells I and 2 may remain in permanent air-tightcontact with each other, during the op# eration of the device, or selected portions ofthe edges of the flanges of said shells may intermittently separate from each other very s1ightlydur ing such operation, to permit air waves to pass between the temporarily separated selected por` tions of said edges or flanges. Likewise, in every embodiment, theinner diaphragm or diaphragms may permanently divide the interior of the device into separate air columns which do not communicate with` each other at any time, or said v diaphragm may iiex, in order to` permit temporary and" intermittent communicationA between said air columns.

Preferably, selected portions of the edges `of,

the shells do separate temporarily and intermittently, While the sound Waves are produced and the diaphragm or diaphragms do temporarily and intermittently permit communication with respective air columns, while the sound waves are produced.

In the embodiment of Figs. 28 and 29, the design` follows the, principle of Fig. 8. The mouthpiece 50 of shell 2 has three ribs 5I which are fixed.

to the inn-erwall of said mouthpiece 50. The respective angles between said ribs are equal, so that in a horizontal plane, their bottom ends are spaced by angles of Said ribs are of streamline shape, so as to offer minimum resistance to air which liows upwardly through mouthpiece 5I). Said ribs 54| have a common center member 52, to which the iiat disc-shaped central part'of the metal diaphragm 1 is fixed. Said diaphragm 1 has a plurality of circular corrugations 56.

The baifie 55 is fixed to the shell I by ribs 54a, providing a channel 54.

lThis Vchannel 54 is oftapered shape so that its volume increases exponentially towards outlet throat 53 of shell I.

` The corrugations `5t of the thin conical diaphragm 1, break up its surface into a plurality of l Since the" diaphragm 1 is rigidly interior wall of said hollow body to normally separate the interior space of said body into an inlet chamber which communicates only with said inlet opening and an outlet chamber which communicates only with said outlet opening, each said chamber having a respective air column, said movable part being movable out of said normal position under the force of compression in said air column of said inlet chamber to establish communication between said chambers, said hollow body having a longitudinal axis, said inlet opening and said outlet opening being located at the respective ends of said axis.

10. An acoustic device which comprises a hollow body, said body having an inlet opening and an outlet opening, an arched diaphragm located in said body, one part of said diaphragm being xed to said hollow body, another part of said diaphragm being movable relative to said body, said movable part having an edge-portion, said movable part being biased to a normal position in which its said edge-portion normally abuts an interior wall of said hollow body to normally separate the interior space of said body into an inlet chamber which communicates only with said REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name l Date 705,398 Gustine July 22, 1902 825,610 Olt July 10, 1906 1,548,380 Parsons Aug. 4, 1925 2,072,786 Yager Mar. 2, 1937 2,158,445 Weiss May 16, 1939 2,385,752

Wilson Sept. 25, 1945 

